Process for the manufacture of a tribo-system

ABSTRACT

A tribo-system comprises a first structural component part and a second structural component part which are in dry frictional contact with one another, each through a surface layer. For this purpose, the surface layer of the first structural component part is based on oxides or mixed oxides in monoclinic, triclinic or tetragonal crystal structure formed from MeO 6  octahedrons with planar oxygen defects.

This application is a division of Application Ser. No. 08/986,778, filedDec. 8, 1997.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The invention is directed to a tribo-system with a first structuralcomponent part and a second structural component part, wherein thesestructural component parts are in dry frictional contact with oneanother, each through a surface layer, and to a process for themanufacture of a tribo-system of this type.

b) Description of the Related Art

The invention relates in particular to the material construction oftribo-systems (friction systems) in the aviation and aerospace industrythat operate without liquid lubricants or lubricating grease and whosestructural component parts are loaded by temperatures of up to 2000° C.,for example, in reusable launchers, hypersonic airborne vehicles andhypersonic aircraft, reentry airborne vehicles and in high-temperaturecomponents or components in the hot part of propulsion units such as,e.g., aircraft engines.

All known liquid lubricants are thermally unstable in air above acontinuous sump temperature of 200° C. and at temporary temperaturepeaks above 350° C. and pass into the gaseous phase at temperaturesabove 400° C., so that they are scarcely usable except as disposablelubricants, although this is to be avoided for ecological-toxicologicalreasons.

Efforts continue to be made to provide friction locations withlubricants through a gaseous surrounding medium, wherein the lubricantsform lubricating connections with the friction surfaces only uponfrictional contact by decomposition or reaction with these frictionsurfaces. However, substances such as tricresyl phosphate,phthalocyanine or aryl phosphate which are mixed in with the gas requireother operating means with regulating and controlling technology on theone hand and, on the other hand, are also objectionable in ecologicaland toxicological respects to the same extent as the previously knownsubstances.

In the case of high-temperature applications in tribo-systems above 400°C., there has been no shortage of attempts in the past to ensurereliable tribological operation over the long term, for example, byarranging solid lubricants in layers and material matrices or by coatingdirectly with solid lubricants. These attempts did not prove successfulin practice, however, because all of the known intrinsic solidlubricants lose their favorable tribological properties as thesurrounding temperature increases and/or as the oxygen partial pressureincreases. Further, solid lubricants which are arranged in materialmatrices are considerably weakened with respect to their mechanicalcharacteristics and coating capability.

Therefore, tribo-systems used in the aviation and aerospace industrywhich are subjected to structural component temperatures of 700° C. to2000° C. through the heat conduction of friction heat and process heatin the friction locations and which therefore chiefly run dry aregenerally either discarded as unrealizable or are installed in coolerregions following suitable heat sinks and with appropriate thermalinsulation. In the latter case, the resulting constructions are bulkyand accordingly take up excessive space and are also heavy and thereforeuneconomical in terms of weight. Nevertheless, such embodiment forms canusually only be used once for a flight mission and are serviced andrepaired after every use.

The tribological behavior of the materials chiefly used at the presenttime for the material construction of tribo-systems during dry runninglimits the life of the products and systems outfitted with thetribo-system because the extent of wear or wear coefficient of thepairing of materials is too high at >10⁻⁵ mm³ /Nm. Consequently,determined constructions with long wear distance and large allowedtolerances must be used so that the friction locations do not undergoadhesive failure, i.e., so that they do not fuse (or "seize"). Suchmeasures against adhesive failure always increase the wear coefficientwith increasing temperature or, in other words, increase wear and allowonly a short useful life. Other failure criteria determining the life ofthese products are material degradation, especially due to oxidation,phase transition, and creep.

Bearing materials of Cr₃ C₂ -CaF₂ which have wear coefficients greaterthan 5×10⁻⁵ mm³ /Nm at 700° C. have been suggested, for example, for thefriction locations operating at approximately 700° C. in the HERMESspace shuttle. CaF₂, as extrinsic solid lubricant, softens atapproximately 1000° C. and also separates due to the high wearcoefficient when applied as bearing material at temperatures up to 2000°C.

OBJECT AND SUMMARY OF THE INVENTION

The primary object of the invention is to improve a tribo-system with afirst structural component part and a second structural component partwhich are in dry frictional contact with one another, each through asurface layer, such that it can operate reliably without difficulty alsoat high temperatures such as those occurring in propulsion units.

According to the invention, this object is met in a tribo-system of thetype mentioned above in that the surface layer of the first structuralcomponent part is made from a material based on oxides or mixed oxidesin monoclinic, triclinic or tetragonal crystal structure formed of(metal)O₆ octahedrons with planar oxygen defects.

A high-temperature lubrication is achieved by means of the invention inthat at least one surface of the closed tribo-systems which operatewithout liquid lubricant and/or lubricating grease is provided, as asliding or rolling contact, with a novel coating which, due to itsmaterial prerequisites and characteristics, is structurally capable offorming wear-reducing or wear-resistant substances on its own freesurfaces through static oxidation and/or through the oxidation promotedduring tribological loading (tribo-oxidation).

It has been found, according to the invention, that the above-mentionedwear-reducing substances have a low shear strength with shear stressesof less than 100 MPa and are therefore able, during dry running, toabsorb the friction force transmitted between the surfaces movingrelative to one another by means of shearing action within the layersformed by these substances which in the case of liquid-lubricatedfriction points would otherwise normally be carried out in the liquidlubricating film. The mechanism of "tribological" shear in thesesubstances accordingly forms a kind of substitute function capable offunctioning up to temperatures of 2000° C. in place of the shearingaction of a liquid film. Accordingly, a traditional problem relating tohigh temperatures, especially in the field of aviation and aerospace, issolved for the first time in a simple manner by a material applicationin situ.

Thus, according to the invention, specific materials which form softreaction layers on their surfaces and which are at least mostly stablein oxidizing atmospheres and/or in a vacuum are used so that thetribological shear stress in dry running is shifted from the basematerial in the near-surface regions to the oxides or mixed oxides inmonoclinic, triclinic or tetragonal crystal structure formed ofi-(metal)O₆ octahedrons with planar oxygen defects, where shearing iseffected as it is in a liquid lubricant film. Substances with a Vickershardness of less than 8 GPa at room temperature are considered softreaction layers.

The oxides or mixed oxides, according to the invention, in monoclinic,triclinic or tetragonal crystal structure formed of MeO₆ octahedronswith planar oxygen defects are structurally exactly describable phaseswith a defined crystallographic arrangement of atoms of determinedsubstoichiometric oxides. Titanium oxides and vanadium oxides, forexample, in accordance with the formula (metal)_(n) O_(2n-1), where n>4,and tungsten oxides and molybdenum oxides, e.g., according to theformula (metal)_(n) O_(3n-1), where n>6, are formed as embodimentexamples. These metal oxides which are constructed crystallographicallyas (metal)O₆ -octahedrons form, as a characterizing property, on thebasis of planar oxygen defects, crystallographically oriented shearplanes on which lattice slippage occurs already at low shear stressesstarting at approximately 10 MPa.

Substances, for example, with a Vickers hardness of less than 8 GPa atroom temperature are regarded as soft reaction layers or oxides of thesurface coat according to the invention. Already at a temperature of1000° C., the hardness of these oxides decreases to values of less than2 GPa and tends to drop further at temperatures up to 1600° C., whichbenefits the shearing mechanism through plastic flow, which will bediscussed in particular hereinafter.

The most striking advantage of these soft oxides over the previoussolutions according to the prior art consists in that they arechemically stable in air so that their beneficial tribologicalcharacteristics are also not lost as the temperature increases, andtheir formation by the operating conditions of the tribo-systems inquestion, e.g., in flying equipment in the aviation and aerospaceindustry, i.e., at high temperatures of up to 2000° C. and, sometimes,in surrounding atmospheres with reduced oxygen partial pressure, is evenbenefitted. The invention is also further advantageous in that thefriction location need no longer be shifted to cooler regions and thefriction locations can be operated as "hot friction locations" within awide temperature range, which has an advantageous result with respect toweight and leads to a gain in construction volume and is particularlyadvantageous in aviation and aerospace. The wear coefficients ofmaterials forming the structures used according to the invention areless than 10⁻⁵ mm³ /Nm at temperatures above 700° C. and enable thematerial construction of wear-resistant closed tribo-systems.

In addition to the mechanism of crystal slippage, the mechanism ofplastic flow, which will be discussed more fully hereinafter, hassurprisingly also proven advantageous for the above-mentioned uses withrespect to protection against wear, especially when the shear stress ofthe soft reaction layer is less than 100 MPa. Plastic flow occursespecially at temperatures above 1000° C. The substrate material onwhose surface a soft oxide with low shear stress is formed by staticoxidation and/or tribo-oxidation is preferably SiC on which a SiO, isformed, where 1<×<2.

The invention has the further advantage that the novel coating also has,in addition to the wear-reducing effect, a friction-reducing effectwhich benefits the operation of the tribo-system.

A further advantage was found in that the operating conditions in hottribo-systems at high temperatures and low oxygen partial pressuresbenefit the stability of the surface layer according to the invention.

As a result of the invention, determined crystallographic factors of theoxides or mixed oxides used in the surface layer are recognized for thefirst time as suitable for solving the problems relating to friction andwear in hot tribo-systems such as a hot joint, for example.

The entire first structural component part, for example, can, withoutrestrictions, be built directly from materials with or made from thesaid substances of the surface layer according to the invention.However, in accordance with the preferred embodiments, the first and/orsecond structural component part are/is at least substantially made fromC-SiC.

Preferred materials contained individually or in combination at least inthe surface layer of one structural component part or at leastsubstantially forming this surface layer are TiO_(2-X), Ti₅ O₉,gamma-Ti₃ O₅, Ti₉ O₁₇, Ti₁₀ O₁₉, Mo₈ O₂₃, high-V₃ O₅, WO₃, W₂₀ O₅₈,β-NiMoO₄, Ti_(n-2) Cr₂ O_(2n-1), V₀₉₈₅ Al₀₀₁₅ O₂, tetragonal tungstenoxide bronzes and/or vanadium oxide bronzes (M_(x) V₂ O₅).

Generally, surface layers according to the invention, especially surfacelayers of the first structural component part, with oxides or mixedoxides in monoclinic, triclinic or tetragonal crystal structure formedof MeO₆ octahedrons with planar oxygen defects are applied already ascoating material, for example, by thermal spraying or by the CVD or PVDprocess.

However, it is also possible that the surfaces determining thetribosystem according to the mechanism of tribo-oxidation can be formedduring operation directly on structural component parts which, e.g., inaddition, are made entirely of tribologically advantageous oxidic,nitridic, or carbidic substances or mixtures or of substances ormixtures belonging to this group of materials, preferably in the form ofengineering ceramics with other oxides or non-oxides. Surface layers,according to the invention, can accordingly also be formed duringtribological loading by reaction with the surrounding atmosphere, e.g.,as in the case of SiC.

It can further be provided in an advantageous manner that the surfacelayer of the first structural component part is a wear-resistant layer.

In accordance with another advantageous further development of theinvention, extrinsic solid lubricants or mixtures can also be used, inaddition, as materials or coatings for making, coating, or infiltratingthe structural component parts in question.

The substrate materials on whose surface oxides or mixed oxides inmonoclinic, triclinic or tetragonal crystal structure formed from MeO₆octahedrons with planar oxygen defects are formed as reaction layers bystatic oxidation and/or tribo-oxidation can be, for example, HfC, TiC,TiN, Ti (C,N), (Ti, Mo) (C,N), SiC, WC, Cr₂ C₃, etc., especially asthin, passive films. In addition, these substrates are also advantageousbecause they are relatively hard, since their Vickers hardness isgreater than 10 or 15 GPa at room temperature. Great hardness results ina small micro-contact surface (true contact surface) of the parts infrictional contact with one another with the result that the shearingforce in connection with the low shear stress during friction isparticularly low. The tribological action of the surface layer,according to the invention, of the first structural component part withoxides or mixed oxides in monoclinic, triclinic or tetragonal crystalstructure formed from MeO₆ octahedrons with planar oxygen defects isaccordingly further enhanced. Under the operating conditions aimed forin the hot tribo-system, the structures used according to the invention,for example, can be formed preferably already by means of the staticoxidation of the hard substrate material or, at the latest, byfriction-induced oxidation with the oxygen-containing surroundingatmosphere. The substrate materials mentioned herein can fundamentallyalso determine the surface layer of the second structural component partor can be contained therein.

The surface layer of the second structural component part is preferablybased on SiC or HfC. This is advantageous because there is often a SiClayer, for example, on the corresponding structural component part as anantioxidation layer. The same advantage is provided when an intermediatelayer, preferably based on SiC or HfC, is arranged between the surfacelayer of the first structural component part and the first structuralcomponent part.

A closed tribo-system is always formed of two solid bodies which contactby their surfaces at determined contact locations; this is what is meantby a tribological pairing of materials. The materials indicated assubstrates and reaction layers are ultimately ceramic materials whichcan sinter without pressure at temperatures above 1100° C. Since the twosurfaces of the parts in frictional contact with one another makecontact, a fusing or sintering together must be expected at operatingtemperatures above 1100° C. (when the increase in temperature caused byfriction is taken into account, a temperature of approximately 800° C.can already be assumed). This can be prevented through the use of theinvention when the materials of the tribo-pairing are not soluble ineach other metallurgically and/or the sintering temperatures lie abovethe operating temperature.

The surface layer of the first structural component part can alsocontain filler materials such as TiO₂ and/or oxides different than theoxides or mixed oxides in monoclinic, triclinic or tetragonal crystalstructure formed from MeO₆ octahedrons with planar oxygen defects. Theseother oxides can preferably contain titanium oxides, vanadium oxides,tungsten oxides and/or molybdenum oxides such as, e.g., TiO_(2-x), Ti₅O₉, gamma-Ti₃ O₅, Ti₉ O₁₇, Ti₁₀ O₁₉, Mo₈ O₂₃, high-V₃ O₅, WO₃, W₂₀ O₅₈,β-NiMoO₄, Ti_(n-2) Cr₂ O_(2n-1), V₀₉₈₅ Al₀.015 O₂ tetragonal tungstenoxide bronzes and/or vanadium oxide bronzes (M_(x) V₂ O₅) or acombination thereof. However, these oxides differ, especially in phaseor structure, from the oxides or mixed oxides in monoclinic, triclinicor tetragonal crystal structure formed of MeO₆ octahedrons with planaroxygen defects which, according to the invention, are compulsorilycontained in the surface layer of the first structural component part orform this surface layer and which possibly have the same composition.

Another advantageous further development of the invention consists inthat the oxides or mixed oxides of the surface layer of the firststructural component part in monoclinic, triclinic or tetragonal crystalstructure formed of MeO₆ octahedrons with planar oxygen defects have ashear plane structure.

Further, additives for improving adhesion can preferably be contained inthe surface layer of the first structural component part and/or in thesurface layer of the second structural component part.

The surface layer of the first structural component part advantageouslyhas a thickness of at least 1 μm.

According to another advantageous construction of the invention, theoxides or mixed oxides of the surface layer of the first structuralcomponent part in monoclinic, triclinic or tetragonal crystal structureformed of MeO₆ octahedrons with planar oxygen defects are stable up totemperatures above 400° C., especially up to temperatures above 800° C.,preferably up to temperatures above 1200° C., and especially preferablyup to 1600° C., and/or remain in the solid state in the indicatedtemperature ranges. The thermal stability range of the structure of thesurface layer according to the invention extends from approximately-100° C. to approximately 1600° C. and even beyond this with somematerials.

The invention also comprises a process for manufacturing tribo-systems,in which regard several process steps and aspects of the process havealready been indicated in the preceding. Accordingly, it is provided byway of example and in an advantageous manner that the surface layer ofthe first structural component part is applied to the first structuralcomponent part or, if required, to the intermediate layer, by CVD, PVDor thermal spraying. Further, as an alternative to this or incombination therewith, the first and/or the second structural componentpart can be produced by a gradient CVI process. A further advantageousconfiguration of the process is provided in that the surface layer ofthe second structural component part is preoxidized before beingarranged in the tribo-system.

The invention is described more fully hereinafter by way of example withreference to embodiment examples in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a basic sectional view of a bearing with a tribo-system;

FIG. 2 shows a schematic enlarged sectional view of a first embodimentform of a tribo-system according to the invention with two structuralcomponent parts in frictional contact;

FIG. 3 shows a schematic enlarged sectional view of a second embodimentform of a tribo-system according to the invention with two structuralcomponent parts in frictional contact;

FIG. 4 shows a schematic enlarged sectional view of a third embodimentform of a tribo-system according to the invention with two structuralcomponent parts in frictional contact;

FIG. 5 shows a schematic enlarged sectional view of a fourth embodimentform of a tribo-system according to the invention with two structuralcomponent parts in frictional contact; and

FIG. 6 shows a schematic enlarged sectional view of a fifth embodimentform of a tribo-system according to the invention with two structuralcomponent parts in frictional contact.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The bearing 1 shown in FIG. 1 comprises an articulated connection andcontains a bearing cage 2 which is constructed in the manner of aquarter-turn fastener for the installation of a two-part bearing shell3, wherein the bearing shell 3 is formed of correspondingly shapedbearing shell halves 3a and 3b. The two-part bearing shell 3 facilitatesmounting on a shaft 4 with a spherically curved bearing surface 5 whichmakes it possible to absorb radial and axial loads. Means forintroducing force 6 are rigidly connected with the bearing cage 2. Allof the parts and elements of the bearing I that are mentioned above areproduced in the shown embodiment example from C-SiC material by agradient CVI process.

The bearing shell 3 and the portion of the bearing shaft 4 containingthe spherically curved bearing surface 5 form a tribo-system 7. FIGS. 2to 6 show enlarged schematic sectional views through differentembodiment forms of the bearing shell 3 and bearing shaft 4 in a regionin which the surfaces of these components are in dry frictional contactwith one another, i.e., no lubrication takes place.

As can be seen from FIGS. 2 to 6, the bearing shell 3 or each of thebearing halves 3a and 3b as first structural component part of thetribo-system has a surface layer 8 which contains oxides or mixed oxidesin monoclinic, triclinic or tetragonal crystal structure formed of MeO₆octahedrons with planar oxygen defects as a wear-resistant layer for thesubstrate material of the bearing shell 3.

In the present case, the surface layer 8 of the first structuralcomponent part of the tribo-system forming the bearing shell 3 containsoxides in triclinic crystal structure formed of MeO₆ octahedrons withplanar oxygen defects such as, e.g., TiO_(2-x), Ti₅ O₉, gamma-Ti₃ O₅,Ti₉ O₁₇, or Ti₁₀ O₁₉. But other oxides or mixed oxides such as, e.g.,Mo₈ O₂₃, high-V₃ O₅, WO₃, W₂₀ O₅₈, β-NiMoO₄, Ti_(n-2) Cr₂ O_(2n-1),V₀.985 Al₀.015 O₂, tetragonal tungsten oxide bronzes and/or vanadiumoxide bronzes (M_(x) V₂ O₅) are also suitable and can be contained inthe surface layer 8.

In the embodiment forms of the tribo-system shown in FIGS. 3 and 4, thebearing shaft 4 forming the second structural component part of thetribo-system also has a surface layer 9 based on SiC. Another oradditional material for this surface layer 9 could also be, for example,HfC.

As can be seen from FIG. 4 in the embodiment of the tribo-system showntherein, an intermediate layer 10 is arranged between the surface layer8 of the first structural component part 3 and the first structuralcomponent part 3 itself, this intermediate layer 10 is based on SiC likethe surface layer 9 of the second structural component part 4. Othermaterials are also suitable for this purpose, wherein only HfC ismentioned by way of example.

In the embodiment presently under discussion, a layer applied bychemical vapor deposition for protection against oxidation of theCVI/C-SiC structure material is used as SiC. This SiC layer alreadysimultaneously forms the friction layer in the second structuralcomponent part and, in the first structural component part 3, forms thesubstrate surface for the tribo-coating of its surface.

SiC or HfC is particularly well-suited as a substrate for thesetribo-layers because the high degree of hardness leads to a small truecontact surface (micro-contact surface) resulting in only a smallshearing force or friction force The hardness of SiC is stillapproximately 5-6 GPa at 1600° C.

It has been found that the tribo-oxidation, for example, in SiC, canserve as a lubrication and wear-resistance mechanism which acts at roomtemperature in dry air already starting from 50 Pa oxygen partialpressure and is promoted by increasing surrounding temperature In thisrespect, it is assumed that SiC partially decomposes into silicone andgraphite, e.g., at 1600° C., at the surface of the structural componentpart. For use in a hot joint or generally in a tribo-system, this meansthat effective and favorably acting lubrication and wear-resistancemechanisms are accordingly available, for example, with tribo-oxidationand the possible graphite formation on the SiC surface for allconceivable operating conditions such as low and elevated temperaturesand low oxygen partial pressures and standard atmosphere.

When the SiC in the friction location is preoxidized before assembly,e.g., in the case of a propulsion unit on the ground, it is expectedthat the wear reserve of the soft reaction layer will be sufficient,with respect to tribology, for one mission starting in a low vacuum.

Another design possibility for the tribo-system which is shown in FIG. 5consists in that the surface layer 8 of the first structural componentpart 3 contains fillers 11 such as TiO₂ and/or oxides different from theoxides or mixed oxides in monoclinic, triclinic or tetragonal crystalstructure formed of MeO₆ octahedrons with planar oxygen defects. Suchoxides can be titanium oxides, vanadium oxides, tungsten oxides and/ormolybdenum oxides. The following materials, which are used in this layerin any case, are especially suitable: TiO_(2-x), Ti₅ O₉, gamma-Ti₃ O₅,Ti₉ O₁₇ or Ti₁₀ O₁₉, Mo₈ O₂₃, high-V₃ O₅, WO₃, W₂₀ O₅₈, β-NiMoO₄,Ti_(n-2) Cr₂ O_(2n-1), V₀.985 Al₀.015 O₂, tetragonal tungsten oxidebronzes and/or vanadium oxide bronzes (M_(x) V₂ O₅) or combinationsthereof.

In order to improve adhesion, the surface layers 8 and 9 of the twostructural component parts 3 and 4 of the variant of the tribo-systemshown in FIG. 6 contain additives 12. However, it is also possible,especially depending upon the intended use of the tribo-system and theconditions pertaining to this use as well as on the materials andcombinations of material used, to use suitable additives in only one ofthe two surface layers 8 or 9, or different additives in each.

The surface layers 8 and 9 of the two structural component parts 3, 4contain materials which are at least substantially insolublemetallurgically in one another. Alternatively, it is possible that eachor both of the surface layers is or are made entirely from suchmaterials. These materials are so selected that their sinteringtemperatures are at least substantially above a maximum operatingtemperature of the bearing 1.

In technical respects relating to manufacture, the surface layer 8 ofthe first structural component part 3 is applied to the first structuralcomponent part 3 or, if required to the intermediate layer 10, by meansof CVD, PVD or thermal spraying. The surface layer 8 has a thickness of1 μm or more. The oxides or mixed oxides of the surface layer 8 inmonoclinic, triclinic or tetragonal crystal structure formed of MeO₆octahedrons with planar oxygen defects have a shear plane structure. Theshear stress of the surface layer 8 of the first structural componentpart 3 is less than 100 MPa in the embodiment forms shown in FIGS. 2 to6.

When using suitable materials, the oxides or mixed oxides of the surfacelayer 8 of the bearing halves 3a, 3b are stable up to temperaturesgreater then 1600° C., e.g., 2000° C., and remain in the solid state.However, depending upon the required use specifications, surface layerscan also be formed which are stable and/or remain in the solid state,e.g., up to 400° C. or up to 800° C. or up to 1200° C.

However, the surface layer 9 of the second structural component part 4can also be preoxidized before the second structural component part,i.e., the bearing shaft 4, is mounted in the tribo-system.

In individual further constructions, the oxides or mixed oxides can beused in the following ways:

a) Coating with materials forming oxides or mixed oxides in monoclinic,triclinic or tetragonal crystal structure formed of MeO₆ octahedronswith planar oxygen defects:

A material which is resistant to high temperatures, e.g.,carbon-fiber-reinforced CVI-SiC which is coated with a SiC layer forprotection against oxidation at the friction location, serves as asubstrate at the friction location. A further tribo-layer comprising,e.g., TiC or other suitable substrate materials, is applied to this SiClayer at the friction location by means of thermal spraying, CVD or PVD.The tribologically active reaction layers are formed either by theaction of the tribological loading as a chemical reaction at the surfaceof the material between the material and the surrounding medium oralready by means of static oxidation. In sliding bearings, only thefriction surfaces of the inner bearing shell and those of the bearingpin are coated, whereas, in a roller bearing construction, at least (or,as the case may be, only) the running surfaces of a corresponding innerand outer ring are coated.

b) Coating with materials forming soft oxides

A material which is resistant to high temperatures, e.g.,carbon-fiber-reinforced CVI-SiC which is coated with a SiC layer forprotection against oxidation at the friction location, serves as asubstrate. The soft, tribologically acting reaction layer is formed onthis SiC layer as protection against wear either as a result of thetribological loading as a chemical reaction of the material surface withthe surrounding medium or already by static oxidation. Accordingly, forthe first time, the SiOx layer forming on the SiC, apart from its actionas an antioxidation layer, is also provided as a tribo-layer suitablefor high-temperature loading. In a sliding bearing construction, onlythe friction surfaces of the inner bearing shell and/or of the bearingpin need be coated.

c) Solid materials

The coatings can be replaced at the friction locations by monolithicmaterials of the described type. In so doing, bearing shells or bearingbushes of one or more pieces are integrated in the structural parts inthe region of the tribo-system that are formed of materials which areresistant to high temperatures. When constructed as a roller bearing, atleast the inner and outer rings are formed of the materials of thedescribed type.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. A process for the manufacture of a tribo-system,comprising the steps of:providing a first structural component part;providing a second structural component part having a surface layerthereon; applying by means of chemical vapor deposition, physical vapordeposition or thermal spraying a surface layer to the first structuralcomponent part or to an intermediate layer arranged on the firststructural component part, said surface layer of said first structuralcomponent part being made from a material based on substoichiometricoxides or mixed oxides in monoclinic, triclinic or tetragonal crystalstructure formed of MeO₆ octahedrons with planar oxygen defects, whereMe is a metal; and providing the respective surface layers of said firstand second component parts in dry frictional contact with one another.2. The process for the manufacture of a tribo-system according to claim1, wherein the first and/or second structural component part is producedby a gradient chemical vapor infiltration process.
 3. The process forthe manufacture of a tribo-system according to claim 1, furthercomprising the step of preoxidizing the surface layer of the secondstructural component part before the first and second structuralcomponent parts are provided in dry frictional contact with one another.4. A process for the manufacture of a tribo-system having first andsecond structural component parts, said first and second component partshaving respective surface layers that are in dry fractional contact withone another, said surface layer of said first structural component partbeing made from a material based on substoichiometric oxides or mixedoxides in monoclinic, triclinic or tetragonal crystal structure formedof MeO₆ octahedrons with planar oxygen defects, where Me is a metal,said method comprising the step of applying the surface layer of thefirst structural component part by means of chemical vapor deposition,physical vapor deposition or thermal spraying to the first structuralcomponent part or to an intermediate layer arranged on the firststructural component part.
 5. The process for the manufacture of atribo-system according to claim 4, wherein the first and/or the secondstructural component part is produced by a gradient chemical vaporinfiltration process.
 6. The process for the manufacture of atribo-system according to claim 4, further comprising the step ofpreoxidizing the surface layer of the second structural component partbefore the first and second structural component parts are provided indry frictional contact with one another.